1. This invention relates to a method for locating circuit to circuit faults in a telecommunications network and also to a fault location system for locating circuit to circuit faults in the terminating circuits of a telecommunications network.
2. Related Art
A conventional public telecommunications network comprises a relatively small number of interconnected main switches and a much larger number of local switches, each of which is connected to one or two main switches. The local switches are connected to the terminating circuits of the network and the far ends of these circuits are connected to terminal equipment such as telephone instruments provided for users of the network. The network formed from the main switches and local switches is known as the core network while a network formed from the terminating circuits is known variously as an access network or a local loop. In this specification, it will be referred to as an access network. Some terminating circuits are connected to a remote concentrator, which may or may not have switching capability. The remote concentrator is then connected to a local switch. In this specification, the term "local switch" is to be interpreted to cover both local switches and remote concentrators.
In a conventional access network, each terminating circuit is formed from a pair of copper wires. Typically, each pair of copper wires passes through a series of nodes between the local switch and terminal equipment. Examples of such nodes are primary cross-connect points, secondary cross-connect points, distribution points and joints.
Unfortunately, terminating circuits are prone to faults. In the case of a terminating circuit carried by a pair of copper wires, example of such faults are disconnection, a short circuit between two wires of a pair of wires and a short circuit between one of the wires and earth. In the case of a conventional access network formed from pairs of wires, the causes of the faults include ingress of water into a node and also physical damage to a node.
Local switches are each provided with a line test apparatus which may be used to test its terminating circuits. Such test systems are useful for detecting and locating faults in individual terminating circuits. However, the present practice suffers from the disadvantage that current line test apparatus are notoriously bad at correctly locating pair-pair faults. Current techniques involve testing only one pair. The measurements on a pair suffering from a circuit to circuit fault can determine that a fault exists, but they cannot give any indication as to the location of the fault within the access network. It is time consuming for an engineer to have to open several nodes before locating and repairing a fault. Furthermore, as the nodes are of a delicate construction, each time an engineer opens a node he may damage the node with the result that there is another fault on a terminating circuit.